In deep hole drilling systems, modern machine tools have led to the need for tooling that can effectively produce holes with a large depth to diameter ratio.
For making large diameter deep holes, the tooling that has been used does not account for using modern machine tools with less available horsepower. The machine tools that are found in use today generally have less available horsepower and can only reach that available peak horsepower at high spindle speeds. Conventional deep hole drilling may utilize double effective cutting geometry where both edges share an equal amount of the cutting load. This type of geometry allows for a drill to establish a centerline and act as a guide for the rest of the drill body following it. This enables longer drill bodies to drill straighter holes without leading off of centerline. In order to achieve chip formation in a way that chip evacuation at depth is manageable, these types of drill would need to be run at heavy feed rates in order to segment the chips. Furthermore, the drill would require being rotated at a relatively low spindle speed to manage the heat at the OD of the tool.
Another style of deep hole drilling that may be utilized is single effective gun drills or ejector head drilling tools. These types of tools are more suited to higher depth to diameter ratios and often require special machines and set-ups to be effective. These types of tools may also utilize a bearing surface on the tool body to attempt to provide stability to the front of the drill by making contact with the inside wall of the hole just previously drilled. This technology is widely used throughout the industry to attempt to provide stability to longer drills or to attempt to keep them drilling on center. It would be desirable to provide tooling that allows simple and flexible set-ups and use of standard machine tools.
Attempts to use a large spade blade to drill deep holes have also been pursued. However, these tools run at lower speeds and higher feed rates. Lower speeds mean that the machine is operating at the lower portion of the machines power curve. Higher feed rates require more thrust which may not be available on modern drilling machines. Indexable Carbide (IC) drills may be used to drill holes at high spindle speeds and lesser feeds. An IC drill will consume less thrust and will run at the higher end of the power curve relative to a spade drill of the same diameter. However at depths greater than 4× Diameter, IC drills lack stability and tend to lead off center which produces a hole that may not meet straightness requirements. Indexable inserts are available in various shapes and have the ability to be rotated (or indexed) to a fresh cutting edge when worn, and eventually replaced. This offers the ability to reuse the tool body any number of times by replacing the worn inserts. The drill body includes pockets to position the inserts by means of a screw or mechanical clamping mechanism. The position of the pocket on the cutting end of the drill body determines the size of the hole to be drilled. These types of drills are considered single flute effective, meaning that the inserts overlap. One insert cuts a portion of the diameter from the major diameter in towards the centerline and the other inserts cut the remaining portion from the centerline out to the point where it overlaps with the other insert.
There is a need to provide tooling that allows for utilizing the power curve of the modern machine tools, while accommodating the desire to drill at higher speed rates and lighter feed rates, but ultimately higher penetration rates.